In recent years there has been a growing awareness of the need to render normally flammable organic materials less combustible. Prior art attempts to reduce the combustibility of such compositions by the incorporation of additives such as halogenated alkyl phosphates, halogenated bi-phenyls, halogenated bi-phenyl ethers, phosphine oxides, polyphosphates, halogenated copolymers, and certain polyphosphazenes have succeeded in varying degrees in achieving an acceptable level of flame resistance; however, this has usually been accompanied by degradation of one or more of the desirable properties of the polymer. Thus, many potentially suitable flame retardant candidates have proven unacceptable because of the tendency of these compounds to catalyze hydrolytic degradation reactions when present in the high concentrations required to impart flame retardancy. Such degradation results in overall polymer destabilization which is manifested by a severe drop in intrinsic viscosity (I.V.) and thermal stability. This problem is particularly acute when blending has been attempted in the melt or at other elevated temperatures. Attempts to circumvent this problem by padding have met with limited success because many flame-retardants have a tendency to migrate during the drawing process thereby producing a non-homogeneous distribution which has the effect of lowering the flame retardant activity and causing deposits on critical roller surfaces. Furthermore, padding generally increases both the cost and complexity of processing because of the additional ovens, baths, and solvent stripping steps that are required.
The introduction of flame retardant agents through copolymerization has proven to be only marginally successful. It has been observed, that the products formed generally exhibit a loss in properties such as a lowered softening point temperature. Cost is also adversely affected by this approach because of the almost certain modification of processing variables that result.
Certain polyphosphazenes have heretofore been utilized in prior art as illustrated by U.S. Pat. Nos. 2,681,295; 2,853,517; 3,193,397; 3,316,330; 3,356,769; 3,392,214; 3,450,799; 3,505,087; 3,792,117, 3,859,249; 3,867,186; 3,869,294 and 3,877,952.
It is therefore an object of the present invention to provide a flame retardant polyphosphazene compound capable of being blended with a normally flammable material without appreciable degradation of any of the properties of said normally flammable material resulting from thermal or hydrolytic instability.
It is a further object of the present invention to provide a process for the production of a polymeric flame retardant composition which exhibits extremely high critical oxygen concentration (hereinafter C.O.C.) values as a result of the particular phosphazene compounds incorporated therein.
It is still a further object of the present invention to provide polyphosphazene containing compositions which are flame retardant, economically acceptable, and effectively nonflammable at low levels of concentration of the particular polyphosphazene compound incorporated therein.
It is still another object of this invention to provide a polyphosphazene containing composition capable of functioning as a flame retardant in both the gas and bulk phase.
These and other objects, as well as the scope, nature, and utilization of the invention will be apparent to those skilled in the art from the following description and appended claims.